| Steel-concrete composite bridge,taking maximum advantage of the material properties of steel and concrete,respectively,has been widely used in the world,and has remarkable technical economic and social benefits.But nowadays,the close-packed I steel girder or steel box girder structures are adopted in construction of composite bridges in China,which costs large amount of steel and needs complex maintenance in their service period.Therefore,it is of great theoretical and practical significance to simplify the structural forms of composite beams,and develop new forms of composite bridges with reasonable forces and economic.In recent years,twin girders or fewer girders with lower stiffening members become the mainstream of the composite bridge in the word,which are especially suitable for urban viaduct and highway construction conditions.There have been existed some engineering application examples in foreign countries,but few in China at present.Therefore,the research on this new type of twin girders or fewer girders composite bridge is of importance in theory and engineering value in application.In this thesis,the theoretical analysis and finite element numerical simulation are carried out on some static mechanical problems of the twin narrow-width box girders composite bridges from the construction stage to the operation stage.And the results can provide some theoretical supports and guidances for the analysis and design of such bridges.The main contents are as follows:1)Based on the existing codes and actual bridge engineering,the parameters were determined and the construction scheme was compiled of a steel-concrete composite bridge with two main narrow-width girders.The finite element software ABAQUS was used to simulate the mechanical properties of the bridge from construction stage to operation stage.On this basis,the deformation and internal forces of the bridge structure system were analyzed and the stress distributions of bridge deck and steel girder in key section were obtained.Also,the shear lag effect and the cracking of the bridge deck were further studied.2)In view of the remarkable bidirectional bending effect of bridge deck of composite bridge with fewer main girders,the system of bridge deck with simply-supported twin main girders was divided in into three sub-decks and two composite beams based on the concept of generalized simple-supported edge and superposition principle.Then,using the boundary and connection conditions between these sub-decks and composite beams,and the analytical series solution of the bending deformation of the bending of bridge deck was obtained.The bending deformation characteristics of bridge deck system of a steel-concrete composite bridge with two main narrow-width girders were studied.It was revealed that the bridge deck has a large transverse hogging moment,which can cause the longitudinal cracking of the bridge deck easily.Besides,the parameter analysis was conducted and the effects of the bending stiffness,length of the bridge deck and the connection performance between deck and steel girder on the deformation and internal forces distributions of the deck were investigated.3)Aiming at problems of controlling the tensile stress at the top of the bridge deck of composite bridge with partially-concrete-filled steel box girder,the box-girder concrete composite bridge was equivalent to a Euler beam with stepped variable stiffness,and the general explicit analytical solution of bending deformation of Euler beams with stepped variable stiffness subjected to arbitrary load was obtained with Heaviside function.In view of a three-span continuous narrow-width box-girder concrete composite bridge in practical engineering,the influences of concrete-filled length and height in hogging moment region of bridge and the wall thickness of box girder on the hogging moment and the tensile stress at the top of the bridge deck were analyzed,and theoretical basis and measures for effective control of tensile stress of concrete bridge deck were provided. |
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